1. Field of the Invention
The present invention relates to a system and method for charging a battery.
2. Background Art
A wide variety of systems and methods exist for charging batteries. They cover the range from charging small batteries used for electronic devices, to nickel-metal-hydride batteries used to power a traction motor in an electric vehicle. Many battery charging methods include the application of a constant current, constant voltage, a combination thereof. These methods tend to be relatively easy to implement; however, they typically cannot be used to charge a battery very rapidly and efficiently. Recently, a number of rapid battery charging systems and methods have been developed.
One such system and method is described in U.S. Pat. No. 5,500,584 issued to Shimomoto on Mar. 19, 1996. The method described in Shimomoto involves the use of a three stage charging process. The second process is where a “quick charging process” occurs. During the second process, a number of current pulses are applied to the battery. The pulses are defined by the application of a large current, followed by a charging suspension. The pulses are applied until a charge-end voltage is attained. One limitation of charging a battery by this method, is that it does not account for changes in battery charge acceptance throughout the charging process, for example, by reducing the current applied to the battery as the voltage gets closer to the charge-end voltage.
Another method and apparatus for charging batteries is described in U.S. Pat. No. 5,680,031 issued to Pavlovic et al. on Oct. 21, 1997. The method described in Pavlovic et al. uses a series of positive current pulses to charge a battery using a charging cycle made up of three different regions. The average current applied to the battery decreases over the three regions. In order to regulate the charging current, the method of Pavlovic et al. uses a value of a resistance free voltage. The resistance free voltage is not measured directly, but rather, requires two different voltage readings, two different current values, and the application of an equation which utilizes the relationship between the voltages, the currents, and the resistance free voltage.
Therefore, a need exists for a system and method for charging batteries that is capable of varying the charge applied to the battery to take advantage of the change in battery charge acceptance, and is capable of doing so using a single, measured parameter without requiring multiple parameter measurements and the application of an equation based on a relationship between the measured parameters.